shivadow

The problem shows as a persistent p1296 even though you have a perfectly fine temp sensor and thermostat.
Its symptoms are an intermittent lumpy engine, mostly after a long run out or heavy labour on the engine (be careful labouring the engine as I found my cv had a weakness and exploded it). At idle it will tick fine and then "bump" every so often. You can hear the bump at the exhaust. The bump is a misfire. These misfires give you p0300, P0301, p0302, p0304. One cylinder will not give a misfire code, i don't know why. For me the cylinder was cylinder 3 (p0303). The bump is accompanied by a flicker of the interior lights.
After a while, starting the engine from cold even on a warm day activates the secondary air injector which is a loudish whistle from the engine bay. Its job is to heat up the catalytic converter. This kicking in most likely is a sign of air induction problems so look at the maf or intake gasket. My car doesn't do this now.
MAF needed a clean and reset via VCDS. 30 quid to fix. Made a world of difference!.
Thanks kentphil, i appreciate your efforts!. Keep up the good work.
I hope this helps someone because it did my head in for weeks on end!.